April 5-7, 2022|Santa Clara Convention Center| Santa Clara, CA

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How to Optimize TxFFE & What We Can Learn From the Optimization


Ransom Stephens  (Consulting Senior Scientist at BitifEye Digital Solutions and Sage at Ransom’s Notes, BitifEye Digital Test Solutions GmbH)


Anton M. Unakafov  (Scientist, BitifEye Digital Test Solutions GmbH)

Sergio Cinà  (Software Developer, BitifEye Digital Test Solutions GmbH)

Wolfgang Kobele  (Software Engineer, BitifEye Digital Test Solutions GmbH)

Hermann Stehling  (Chief Technical Officer and Lead Software Developer, BitifEye Digital Test Solutions GmbH)

Location: Ballroom E

Date: Thursday, April 7

Time: 9:00 am - 9:45 am

Track: 09. High-Speed Signal Processing, Equalization & Coding/FEC, 07. Optimizing High-Speed Link Design

Format: Technical Session

Theme : High-speed Communications

Education Level: All

Pass Type: 2-Day Pass, All Access Pass

Vault Recording: TBD

Audience Level: All

Ever-increasing data rates demand more powerful transmitter feed-forward equalization (TxFFE): more taps and better simultaneous optimization of inter-symbol interference (ISI) correction and of noise. The complexity of tap optimization increases exponentially, each new tap introduces another dimension to the optimization equation. Multi-level modulation schemes like PAM4, PAM8, etc add yet another level of complexity; since tap granularity is limited by the transmitter's digital to analog converter (DAC) resolution, the more symbols, the fewer available tap values per symbol. We begin by reviewing techniques for tuning taps in practice, called link training, and for calibration of TxFFE signals for compliance and diagnostic tests. We then address three important issues: First, the best test points for calibrating TxFFE taps – the transmitter output, the test fixture output, or the input to a compliance board. Second, the most effective patterns for analyzing the properties of TxFFE signals; we'll show the pros and cons of a simple step response versus test patterns that produce ISI to make the TxFFE effect explicit, and the impact of finite DAC resolution for both. And, finally, we consider what optimized TxFFE taps can tell us about the channel, a question pivotal for understanding link training.


Clear and detailed understanding of TxFFE: optimization techniques, limitations imposed by the serdes' digital to analog conversion (DAC) resolution, the impact of noise and of the modulation scheme.

Intended Audience

General familiarity with high speed I/O and signal integrity